1. Field of the Invention
The subject invention is directed to automated systems for container inspection and, more particularly, automated systems for optically inspecting transparent and translucent containers for composition defects.
2. Description of the Prior Art
Various systems for inspecting containers are known in the prior art. Those systems were often used to inspect refillable transparent or translucent containers for foreign materials after the containers were washed, but before they were refilled. However, it was also found that such systems were useful in identifying certain material defects in the containers. Defects such as "stones" (refractory particles) and "seeds" (air bubbles) represented potential failure points and those inspection systems also came to be used by container manufacturers as well as fillers to inspect containers at the time of manufacture.
Generally, in these prior systems a rotating prism projects an image of the bottom of the container through a lens and onto an array of photosensors that are arranged in a fixed circle. Each photosensor is responsive to an area of the container bottom that defines a circular band within the container image. In combination, the circular bands cover the entire area of the container bottom.
One disadvantage of these systems has been that they require precise placement of the container with respect to the rotating prism. Often this positioning is accomplished by a star-wheel mechanism that required costly changeover parts to accommodate containers of different sizes and shapes.
In recent years, improvements in solid-state cameras have led to higher image resolution capability and lower overall cost for inspection systems. Improvements in commercially available vision engines have also allowed more accurate interpretation of such higher-resolution images. In some applications, those improvements have allowed cameras to replace the combination of the spinning prism and photosensor array that was used in prior art inspection systems. Thus, the improved camera technology avoided the requirement for precise positioning of the containers and allowed side-transfer belts to be used to convey the containers over an inspection location. Side-belt conveyors were used because they allowed the container to be viewed through the bottom. The side-belt conveyors were also preferable for the reason that they were mechanically simpler than the star-wheels and did not require parts changes to accommodate different container sizes and shapes.
In detecting defects in the containers, in some applications it was found that the improved sensitivity of the camera inspection system had to be compromised to avoid false positive responses to stippling, identification or decoration that was embossed into the bottom of the container or to avoid confusion with baffle marks, cut off scars or other non-stress related defects. To avoid this problem, a diffused light source sometimes has been used to illuminate the bottom of the container. The diffused light source masks the embossing and glass molding marks found on some containers and makes opaque, stress-related defects easily distinguishable. However, this technique also masks some non-opaque defects that represent potential failure points or that are otherwise objectionable.
In the prior art, inspection systems have attempted to compensate for these shortcomings by distancing the diffuse illumination system from the bottom of the container. This practice was found to make non-opaque defects more apparent, but it also increased the rate of false positive indications caused by permissible irregularities or embossed areas in the bottom of the container.
In some instances, container manufacturers have attempted to overcome the difficulties of false positives in bottom inspection systems by eliminating the use of molding marks on the bottom of the containers. However, that also bars the display of helpful information that can be embossed on the container. For example, binary cavity identification techniques are helpful in correlating container defects with particular mold cavities. This information has been used to improve manufacturing efficiency. However, such techniques generally employ the molding of concentric rings, dots or other binary cavity information into the base of the container. Such mold identification techniques conflict with the use of bottom inspection systems.
As a compromise to eliminating the use of any mold cavity identification system, some manufacturers have employed a heel code system wherein the bar code is embossed on the heel of the container instead of on the bottom. This facilitates the use of a bottom inspection system, but has the disadvantage that it requires that the container must be stopped and rotated to read the code. Moreover, when the container is not round so that it can be easily rotated, such heel code systems are not available.
Accordingly, in the prior art there existed a need for a bottom inspection system that could readily discriminate opaque defects as well as other defects, and that was compatible with established methods for providing the container with cavity mold identification and other information or decor embossed thereon.